[ckissick]

All I know about this is what I read, and two things worth noting are:

1) I've read that ice core data are, in fact, quite inaccurate. When you de-pressurize the air sample, its chemistry changes. Other errors comes in during sampling amd handling. Therefore, the results have a plus/minus component, and the alarmists just report the lower end of the error scale. The upper end of the error scale gets you well above 300 ppm.

2) Even if we have caused CO2 levels to go higher than anytime in the last 800,000 years, some climatologists say, "So what?" CO2 has a very small role in global warming, with maybe 2.5% of warming attributed to CO2. Water vapor is by far the most important green house gas, as red-beard alluded.